The present invention relates to a flow control device of a helically-shaped intake port for use in a diesel engine.
A helically-shaped intake port normally comprises a helical portion formed around the intake valve of an engine, and a substantially straight inlet passage portion tangentially connected to the helical portion. However, if such a helically-shaped intake port is so formed that a strong swirl motion is created in the combustion chamber of an engine when the engine is operating at a low speed under a light load, that is, when the amount of air fed into the cylinder of the engine is small, since air flowing within the helically-shaped intake port is subjected to a great flow resistance, a problem occurs in that the volumetric efficiency is reduced when the engine is operating at a high speed under a heavy load, that is, when the amount of air fed into the cylinder of the engine is large.
In order to eliminate such a problem, the inventor has proposed a flow control device for use in a gasoline engine. In the flow control device, a bypass passage, branched off from the inlet passage portion and connected to the helix terminating portion of the helical portion, is formed in the cylinder head of an engine, and a normally closed type flow control valve, actuated by a vacuum operated diaphragm apparatus, is arranged in the bypass passage and opened under the operation of the diaphragm apparatus when the amount of air fed into the cylinder of the engine is larger than a predetermined amount. In this flow control device, when the amount of air fed into the cylinder of the engine is large, that is, when the engine is operating under a heavy load at a high speed, a part of the air introduced into the inlet passage portion is fed into the helical portion of the helically-shaped intake port via the bypass passage. This reduces the flow resistance of the helically-shaped intake port, thus, enabling high volumetric efficiency. As mentioned above, in the flow control device, since the vacuum operated diaphragm apparatus is used for actuating the flow control valve, a vacuum source is necessary for the diaphragm apparatus. In a gasoline engine, since vacuum is produced in the intake passage of the engine, such a vacuum source is easily available. However, in a diesel engine, since no throttle valve is arranged in the intake passage, vacuum is not produced in the intake passage. Therefore, a vacuum source cannot be easily obtained.